Discharge tube



May 25; 1937. B. KROL DISCHARGE TUBE Filed May 20, 1936 INVENTOR BAARTE KROL Patented May 25, 1937 PATENT OFFICE DISCHARGE TUBE Baartc Krol, Mitcham Junction, England, as-

signor to N. V. Philips Gloeilampenfabrieken,

Eindhoven, Netherlands Application May 20, 1936, Serial No. 80,690 In Great Britain May 28, 1935 2 Claims.

My invention relates to electric discharge tubes, and more particularly to means for supporting various members of such tubes.

My invention is particularly adapted for supporting heating filaments, and I shall describe same in this connection; however it should be understood that my invention is in some cases applicable to the support of other electrodes, for instance a grid formed by a wire wound in zigzag fashion in substantially one plane.

I shall describe my invention in connection with the supports of heating filaments, for example as are used in radio receiving tubes operated from storage batteries.

In present-day battery-operated radio receiving tubes, the filaments are generally formed in zigzag fashion in the shape of a V, -W or similar figure. Although the two ends are suitably supported from the pinch, it is also necessary to support or suspend the filament at those points at which the filament changes its direction, i. e. at the apex or apices of the zigzag winding. Such supports are intended to prevent vibration of the filament, which, as is well known, would cause so-called microphonic noises and increase the allowable electrode spacings. For this purpose it has been proposed to use supporting means, such as hooks, at least one of which is resilient or is provided with a spring to tension the filament, with or without mica spacers which cause a tension in the filament. Such tensioning of the filament is very undesirable, and in addition the use of hooks produces local cooling whereby the electron emission is considerably reduced.

My invention obviates, or at least considerably reduces, such difficulties as have been above pointed out, and provides a simple and efiective support for filaments and other electrodes.

According to my invention a directly-heated filament, for example, is compressively supported, without tensioning, between two or more supports of an electrically-insulating and poorly heat-conductive substance, such as mica or the like, which supports are in turn supported within the tube.

With such a support the electrode spacing, for example, the distance between the filament and grid, may be reduced to a very small value without any difiiculties, while at the same time, due

to the absence of hooks and. the like, and with a suitable design of the supports, the cooling of the filament may be very considerably reduced and tensioning of the filament completely avoided.

In order that my invention may be .clearly understood and readily carried into effect, it will be more fully described with reference to the accompanying drawing, in which:

Figure 1 is a partly sectionized side elevation on an enlarged scale of a portion of a thermionic 5 tube embodying my invention;

Figure 2 is a side View of Figure 1;

Fig; 3 is a sectionized view of Fig. 1 taken along line III-J11;

Fig. 4 is a sectionized View of Fig. 1 taken along 10 the line IV-IV;

Figs. 5 and 6 are side views of supporting members for filaments of other shapes;

Fig. 7 is a perspective view of a complete thermionic tube utilizing my invention. 5

As shown in Figs. 1-4, a directly-heated filament or cathode I0 is arranged in a plane in zigzag formation, and has its ends connected by wires Ii to conductors l2 sealed into a pinch l3 forming part of the evacuated envelope 39 of the tube which is provided with an ordinary base 40 and contact pins 4|, as shown in Fig. '7.

The filament It! is arranged between and supported by two rectangular plates or sheets l4 of an electrical insulating and poorly-heat-conductive material, for instance mica, provided with rectangular apertures l5 through which the major portion of the filament is exposed. The apertures l5 are so shaped and the filament I0 is so positioned therebetween that the points at which the filament changes its direction are gripped or clamped between the two adjacent sheets l4, whereas a portion of the filament between those points is held between the bars I6 remaining between the apertures of each sheet.

The filament is thus held firmly in position without any tensioning thereof.

A filament for use with the present invention may be formed by winding a wire, for instance, in a suitable jig into a zigzag form, flattening the zigzag wire by applying pressure normally to the plane of winding, activating the so-formed zigzag wire, for instance by spraying, and subsequently clamping the wire between the supports and mounting it on the pinch; or alternatively first mounting the wire on the pinch and then clamping it between the supports.

Provided along each vertical marginal edge of the two sheets I4 is a U-section metal stiffener and spacer I1, whereas another U-shaped clip I8 serves to clamp the sheets together and also to firmly hold the connecting wires II and maintain them accurately in position.

The mounting of the two sheets [4 is effected by clamping each vertical edge thereof, with the are mounted in metal supports 20 sealed into the pinch l3. As shown, the clamping strips [9 are formed as two opposing strips which are spot-welded together at their ends, however a single strip bent back upon itself may be used for this purpose. In addition toacting as supports the clamping strip I9 may also serve as leads for the filament connections. Furthermore, the U-section members I! also serve to interspace the two sheets it when these sheets are clamped between the vertical strips I9, whereby the filament it is held snugly at all points without undue pressure, and as a result excessive heat losses at the points of contact between the filament and the supports M are avoided.

The support strips H! are conveniently arranged as part of or the support for, one of the other electrodes of the tube. As shown in Figs. 1-4, the grid structure of the tube consists of a plurality of wires 2! spot-welded or otherwise secured to the inner surface of the vertical strips 19 with the aid of metal strips 22. With such a construction the spacing between the filament and the grid can be reduced to a very small amount without any difiiculty.

Instead of using a grid of the above construction, the grid, or similar structure, may be formed by winding the Wires around the mica sheets I 4 before mounting them between the strips l9 and members H.

In addition to supporting filaments of the shape shown in Figs. 1-4, the invention is applicable to filaments of other shapes.

As shown in Fig. 5, a V-shaped filament 32 having long straight portions is supported between support plates 30. The supports are similar to the supports M of Figs. 1-4 with the exception that they have four rectangular apertures 3i separated by ribs 23.

As shown in Fig. 6, a filament 33 of a spiral shape is supported between plates 34. The plates 34 are similar to the plates ll] of Figs. 1-4 with the exception that they are provided with sectorshaped apertures 35 separated by radially-extending ribs 25. To facilitate bringing out the lead Wires, the filament 33 is formed of a single wire wound double, the ends 36 and 31 of the wire acting as the leads.

Instead of clamping the filament between apertured mica sheets and using the frame construction shown, various other constructions may be used. For instance, the filament may be clamped between pairs of straight mica strips held together at their ends by pairs of E, F, or L-shaped members. Furthermore, in addition to using clamps at the edges of the mica sheets, the sheets may be held together at intermediate points by eyelets, as indicated at 38.

Furthermore, when supporting a grid or other electrode, the clamps on the edges of the mica sheets. may be provided with notches or slots.

In addition to supporting bent filaments of the type shown in the drawing, the invention is also adapted for supporting linear filaments. For example, in the case of a magnetron it may be desirable to support the filament at intermediate points. As in such cases the anode is usually split into two portions, the clamp may extend between these portions.

To increase the active emitting surface and to facilitate clamping, the filament is preferably flattened, i. e. formed as a narrow strip or ribbon.

While I have described my invention in connection with specific examples and applications, I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim is:

1. An electric discharge tube comprising an envelope having a pinch, a filamentary electrode, lead Wires electrically connected to said filament and sealed in said pinch, and means for supporting said electrode from said pinch comprising a plurality of relatively thin perforated plates of electrical insulating material of poor thermal conductivity, said electrode and lead wires. being clamped between said plates with the electrode in registry with said perforations, and a plurality of fastening means for holding said plates together, one of said means being disposed near said lead wires to rigidly hold same between said plates.

2. An electric discharge tube comprising an envelope, a folded filamentary electrode arranged in a plane, a grid electrode, means for compressively supporting said filamentary electrode comprising a plurality of perforated plates of electrical insulating material of poor thermal conductivity, and a plurality of metal supports attached to the edges of said plates for supporting said plates and for holding said plates together, said supports attached to and holding said grid electrode over said perforations in cooperative relation with the filamentary electrode.

BAARTE KROL. 

